Active matter refers to a class of non-equilibrium systems in which individual particles are self-propelled due to an irreversible consumption of energy. Their physics is relevant to systems ranging from biological to man-made materials [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}.
They have attracted much attention since they exhibit a host of novel collective behaviors which cannot be found in equilibrium systems. Examples range from the transition to collective motion, through low-Reynolds turbulence, to motility-induced phase separation (MIPS) [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]}, [16]}, [17]}, [18]}, [19]}, [20]}, [4]}, [22]}, [23]}, [24]}, [25]}, [26]}, [27]}, [7]}. The latter corresponds to the ability of active systems to phase separate, even when there are no attractive interactions between the particles.
